Cooling Down in Motown
New superconducting cables are put to the test in Detroit.
A gritty section of Detroit surrounds one of the city’s oldest electric power stations. But the technology that Detroit Edison is installing at the Frisbie substation is pure 21st century-underground superconducting cables that can transmit immense currents of electricity with near perfect efficiency.
While increasing energy demands are putting more and more stress on the nation’s long-distance power transmission network, cities are suffering their own version of electric gridlock; in many locations, underground transmission lines are fast reaching capacity and are literally burning up. Superconducting cables, like the ones being installed in Detroit, could safely triple the power moving through existing conduits, avoiding the need to dig up the streets-even making room for fiber-optic communications lines.
The Frisbie demonstration marks a milestone in electricity know-how-one of the first commercial applications of high-temperature superconductors. These ceramics, first fashioned by IBM researchers in 1986, now transmit alternating currents with nearly zero resistance at temperatures as high as -139 C (the
materials can be cheaply cooled to that temperature using liquid nitrogen). In contrast, conventional copper cables dissipate as much as 10 percent of the power they carry because of resistance; that lost power escapes as heat, which limits just how much juice can flow before the cable melts.
American Superconductor, the firm making the materials being tested in Detroit, has been trying to find real-life uses for the ceramics since it was founded in 1987 by MIT materials scientists Greg Yurek and John Vander Sande. Their trick is to fabricate the superconductor as flexible conductive tapes. Pirelli Cables and Systems, the world’s largest producer of power cables, wraps the tape with insulation and a protective sheath on the outside and a channel up the middle for the liquid-nitrogen coolant, which keeps the tape in superconducting mode.
Surrounded by shuttered buildings and empty lots, the Frisbie station has plenty of spare capacity-meaning its 13,500 customers won’t be left in the dark if the superconducting cables fail. But Detroit Edison is already looking at using the technology to replace overloaded conventional cables serving busier sections of the city.
And Pirelli R&D manager for superconductivity Marco Nassi says success in Detroit should lead to commercialization of superconducting cables elsewhere “within the next few years.” Because the superconducting materials still must be cooled down to liquid-nitrogen temperatures, applications are likely to be limited to relatively short-range trans-mission in underground cables, rather than long-distance transmission. But that could still be a savior for a number of cities whose maxed-out underground transmission systems are literally burning up.
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